Liquid treatment of contact surfaces for copper oxide rectifiers



Patented Mar. 22, 1949 CROSS REFERENCE LIQUID TREATMENT OF CONTACT SUR-FACES FOR COPPER OXIDE RECTIFIERS Carl C. Hein, Pittsburgh, Pa.,assignor to Westinghouse Electric Corporation,

East Pittsburgh,

Pa., a corporation of Pennsylvania No Drawing. Application May 7, 194.6,Serial No. 667,989

1 Claim. 1

My invention relates to dry contact rectifiers and, in particular,relates to methods of making good electrical contact to the oxidesurface of copper oxide rectifiers.

As is disclosed in Grondahl Patent No. 1,640,- 335, the junction betweenmother copper and a cuprous oxide layer formed thereon constitutes avery effective current rectifier, but commercial employment of suchrectifiers has emphasized the problem of making electrical contact tothe outer surface of the cuprous oxide which shall have a relatively lowresistance to current flow in the normally conductive direction and inwhich the value of the voltage drop due to current flow shall berelatively constant during the life period of the rectifier. Variousmethods of making electrical contact to the oxide surface have beenproposed, for example, lightly abrading the oxide surface by means of asand blast or the like and superposing thereon a thin layer of silver,gold or other metal by evaporation and condensation.

However, when the san lasting method is used on rectifiers, particulafor relatively high voltage service, it is found that the disturbance tothe delicate inter-face between the oxide and the copper is likely torender the rectifiers susceptible to electrical breakdown.

In accordance with my present invention, I avoid the difficulties fromabrading the oxide surface before deposition of the metallic layer byvarious other types of treatment.

One object of my invention is, accordingly, to produce an improvedmethod of making electrical contact to the oxide surface of copper oxiderectifiers.

Another object of my invention is to provide a method of forming contactlayers of evaporated or sprayed metal on the oxide surface of copperoxide rectifiers which avoids damage to the rectifier by employment ofabrasion or the like prior to such metallic deposition.

Still another object of my invention is to provide an improved method ofpreparing the oxide surface of copper oxide rectifiers for deposition ofa metallic contact layer.

Other objects of my invention will become apparent'upon reading thefollowing description of processes embodying the principles of myinvention.

In order to prepare copper oxide rectifiers for the use of my process,they are first oxidized in an atmosphere containing oxygen at atemperature not far below their melting point; and subsequently annealedat a temperature of the order of 500 to 600 degrees for a period of theorder of 15 minutes and then cooled either in air or water to roomtemperature. This treatment leaves a layer of cuprous oxide adjacent tothe copper and superposed on such layer a coating of black cupric oxide.The latter is preferably removed by etching for 2 minutes in 2% sulfuricacid at C., followed by a quick dip in concentrated nitric acid and asubsequent rinse in tap water and drying.

The oxide surfaces so prepared are then dipped for a period of from oneto five minutes in a mixture of ammonium hydroxide of specific gravity0.9015 with water, the ammonium hydroxide being from 12 to of themixture.

In accordance with another form of my invention, the oxide surface maybe dipped in a solution containing equal parts of ammonium hydroxide,specific gravity 0.9015, and hydrogen peroxide, such immersion beingcontinued from one-quarter of a minute to six minutes.

In accordance with another embodiment of my invention, cuprous-oxidesurfaces, prepared as above described, are mounted on a rotatablespindle and a piece of soft white felt is held against the surfaceduring the rotation.

In accordance with still another embodiment of my invention, therotating oxide surface above described is held against thin felt onwhich very fine carbon black, such as is used in the preparation ofcolloidal graphite materials, had been rubbed.

In still another modification of my invention, the felt used to rub therotating oxide surface was previously dipped into a water suspension ofcolloidal graphite known in the trade as Aquadag.

In accordance with still another modification of my invention, Aquadagwas applied as a heavy coat to the washer and thereafter washed off withwater.

After employing any of the above-mentioned modifications of myinvention, evaporated silver was deposited on the surface of the treatedcopper oxide by placing the unit in an evacuated container in which abody of silver was heated to the point where it sublimed.

I tested rectifier units coated with a conducting layer in accordancewith each of the abovedescribed methods to determine whether they wereafl'ected during a long active life by humidity or moisture and foundthat their resistance in the conductive direction was substantiallyinvariable over periods up to 500 hours. In this gen peroxide.

CARL C. HEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS N; Name Date 954,984 Mertz Apr. 12, 1910 1,037,469Goldberg Sept. 3, 1912 1,353,654 Harrison Sept. 21, 1920 1,484,690Walker Feb. 26, 1924

